Glass metal seal



Patented Dec. 1, 1936 UNITED STATES PATENT; OFFICE GLASS METAL SEAL No Drawing. Application July 5, 1929,

Serial No. 376,291

14 Claims. (01. 176-36) My invention relates to alloys and particularly to alloys of metalsin the iron group of the periodic table.

One object of my invention is to provide an alloy having a predetermined coeflicient of expansion over a temperature range from substantially room temperature to the annealing temper-- ature of certain glasses, particularly bore-silicate glass and ordinary lead glass.

Another object of my invention is to provide an alloy having a smaller coefllcient of expansion than the nickel-steel alloys.

Another object of my invention is to provide an alloy adapted to form a vacuum-tight seal through bore-silicate glass.

Another object of my invention is to provide an alloy adapted to form a vacuum-tight seal through lead glass.

Another object of my invention is to provide an improved method of sealing electrical conductors through glass.

A further object of my invention is to provide a method for producing a vacuum-tight seal of electrical conductors, having only a limited range of expansivity substantially equal to that of ordinary glasses, through the latter without causing breakage of the seals in cooling to room temperature.

Other objects of my invention will become apparent on reading the following specification.

In connection with the manufacture of vacuum-tight electrical-discharge devices in glass containers, the problem arises of making vacuumtight seals of metals through the glass walls. In forming such seals, a small hole is melted in the glass wall of the container; the metal lead is inserted and the molten glass squeezed around the lead andfused thoroughly in contact therewith. In order that the resulting seal shall not crack or leak after it has cooled, it is necessary that the metal and the glass shall have substantially the same expansivity with temperature over the range from the annealing temperature of glass down to room temperature; and preferably that pansion than lead glass and, consequently, platinum seals could not be used in it. However, tungsten and molybdenum were found to have coefficients of expansion of the right order of magnitude and to form vacuum-tight seals with boro-silicate glass. Such seals are, 'however, rather expensive and not entirely satisfactory.

Platinum, likewise, is an extremely expensive metal and, consequently, composite conductors having cores of nickel-steel. covered by thin jackets of copper were developed, and thus cheaper, but equally satisfactory, seals through ordinary lead glass were obtained. The coefficient of expansion of copper is higher than that of lead glass; and, since the jacket of copper is relatively thin, the nickel-steel alloy employed is one which has a coeflicient of expansion nearly equal to that of lead glass.- Copper is a metal which lead glass "wets readily; and theexpansivity of nickelsteel is slightly less than that of glass over the range of approximately 400 C. between the temperature at which strains readily relieve themselves in lead glass and room temperature.

However, when the attempt was made to find nickel-steels of the low expansivity coresponding to that of bore-silicate glass, it was found that, while this low expansivity existed up to a certain critical temperature, this temperature, herein called the inflection temperature, was considerably lower than that of the nickel-steel alloys suitable for lead glass; and that, consequently, there was a range of temperature just below the proper annealing temperature of the glass in which the expansivity was so great that vacuum-tight seals could not be produced.

In accordance with the present invention, I have discovered that, by substituting cobalt for a certain part of the nickel in the nickel-steels previously employed, alloys result having sufficiently low coeflicients of expansion throughout the entire range below the necessary annealing temperature of bore-silicate glass; that such alloys are we by the born-silicate glass; and that the combination produces satisfactory vacuum-tight seals. Furthermore, I find that, by employing certain other nickel-cobalt-iron alloys, and even certain nickel-iron alloys, seals may be made through ordinary lead glass; and this without the necessity for copper-jacketing the alloy.

In accordance with the foregoing principles, I have found that substitution of cobalt for nickel in nickel-iron alloys results in a decrease of expansivity of approximately 0.5)(10 cm. per cm- Per degree centigrade for each percent of cobalt thus substituted. Ordinary lead glass has an expansivity of approximately 9x10 cm. per cm. per degree C. while boro-silicate glasses have expansivities between 3.0 and '7.0 10 cm. per cm. per degree C. In accordance with the foregoing principles, I have found that alloys containing from 28% to 34% nickel, from 5 to 20%-cobalt and from to 1% manganese, the remainder of the alloy being iron, maintain an expansivity over the temperature range up to the annealing temperature of boro-silicate glass, that is to say, up to about 400 C., which is a sufficiently near approximation to that of the glass to ensure a successfulvacuum-tight seal. In particular, I have found that an alloy comprising 32% nickel, 16% cobalt, 0.8% manganese, carbon up to 0.10% and the remainder iron, may be sealed successfully through borosilicate glass having a coefficient of expansion of substantially 6.2)(10 cm. per cm. per degree C. 7 As examples of such boro-silicate glasses, the following may be given:

1. 72.4% $102; 9.8% NazO; 10.2% 13:03; 5.1% A1203; 1.8% PbO.

2. 67.0% $102; 6.4% NazO; 19.0% 13:03; 1.2% A1203; 4.8% SbOa.

3. 73.8% S102; 18.7% B203; 5.2% PbO; 1.0%

A1203; 0.5% AS203. I have found that successful seals result from the employment of alloys within the ranges of the composition heretofore described in conjunction with either of the aforesaid borosilicate glasses.

I have further found that a successful seal may be made between boro-silicate glass having an effective expansivity between 6.0 and 6.5 '10-- cm. per cm. per degree C. and an alloy containing substantially 27% nickel, 22% cobalt, 0.5% manganese and the remainder iron.

Likewise, I have found that alloys containing from 23% to 28% nickel, 17% to 23% cobalt, 0 to 0.5% manganese and 0 to 0.3% carbon may be sealed successfully in boro-silicate glasses having effective expansivities between 3.0 and 5.5)(10-9 cm. per cm. per degree C. In particular, I' have found particularly good seals to be produced between borosilicate glasses having expansivities between 3.0 and 5.5 10 cm. per cm. per degree C. and alloys containing substantially 29.8% nickel, 15.5% cobalt, 0.22% manganese and 0.3% carbon. Boro-silicate glasses having expansivities of substantially 3.6X10- cm. per cm. per degree C. apparently produce the best seals with the alloy last men-' tioned. g

I have also found that a seal between the hero-silicate glass known to the trade as G702P and manufactured by the Coming Glass Company, seals well with a lead comprising 29.4% nickel, 16.3% cobalt,.0.2% manganese and the remainder iron. I have also obtained excellent seals between the same glass and a lead coated with-chromium or copper and consisting of an alloy containing substantially 23.8% nickel, 21.9% cobalt, 0.2% manganese, 0.3% carbon and the remainder iron.

In general, I have found that, in the case of alloys of low expansivity containing nickel and iron, whether or not they also contain cobalt, it is desirable that the relationship expressed by. the following formula should hold:

It also appears desirable, for most purposes, to minimize the amount of manganese, the maximum percentage of this element being preferably below 0.2%. Carbon, however, appears, in most instances, to be desirable up to the amount of 0.3%, as it prevents a higher cobalt content than would otherwise be desirable and does not seriously affect expansivity.

As previously stated, I have found certain nickel-cobalt-iron alloys to seal successfully into ordinary lead glass having a coefllcient of expansion in the neighborhood of 9 10- cm. per cm. per degree C. For instance, alloys comprising 30% to 45% nickel, to 25% cobalt and 0 to 1% manganese, form satisfactory seals with lead glass having an expansivity between 6 10- and 10 10 cm. per cm. per degree C.

I have found that the preparation of vacuumtight seals between metals and glass is rendered more certain if the metals are annealed in vacuo or in a bath of a fused salt which readily dissolves the oxides of the metal. For example, sodium nitrate is one such salt, many others being known to skilled chemists.

I have also found that a certain amount of trouble is caused in making vacuum-tight seals because of gases released' at a high temperature, and largely results from a reaction between carbon in the metal and oxide formed on the surface I of the metal during heating in air.

When, however, the metal is finished to a small cross-section, the carbon may be removed conveniently from the solid metal. The treatment required is heating at an appropriate temperature in hydrogen or in a fused salt bath containing no great amount of carbon compounds. A bath comprising sodium chloride and 85% barium chloride at from 700 to 1200 centigrade is one suitable bath.

Coating to avoid gas generation at the surface may be readily accomplished by electroytic deposition of a thin layer of chromium or other carbon-free metal provided that the oxygen-carbon relations within the alloy are not such as to cause severe gas release at working temperatures. In the event that gas is evolved without surface oxidation, a treatment, such as that just described, may first be applied to prevent injury to the coating by the gas. This treatment is particularly applicable to plated metals intended for hightemperature service.

The temperature at which strains are readily relieved in glass is, of course, not an absolutely fixed quantity, even for glass of a given chemical composition. At very high temperatures, the

glass is relatively soft and, as the temperature decreases, it hardens. The lower the temperature and, consequently, the harder the glass, the less rapidly it is able to flex and relieve mechanical strains existing within it. However, since the inflection temperature, that is to say, the maximum temperature, at which coefficient of expanslon of the above-described alloys remain low, decreases as the coeflicient of expansion itself is decreased, it is desirable to form seals with as low an annealing temperature as possible. I have found that alloys, in which the inflection temperature is relatively low, may be employed to produce satisfactory seals if the completed seal is maintained at a temperature of about C. above the inflection temperature for a considerable period of time. Thus, while the strains are relieved slowly, they do so progressively and with certainty, and a strong vacuum-tight seal results in the end.

As an example of the softer glasses, referred to above as lead glasses, the following may be taken as typical in composition:

63.1% 810:; 20.2% PbO;v 0.28% A1203; 0.94% CaO; 7.6% Nap; 5.5% K20; 0.88% M11304 The above subject matter is also described and referred to in my copending application Serial No. 376,292, filed July 5, '1929, for Alloys, now Patent No. 1,942,260, issued January 2, 1934.

While I have, in the foregoing, described certain particular embodiments of my invention, it will be understood that-these are for purposes of illustration only, and that the broad principles may be otherwiseutilized, as will be readily apparent to those skilled in the art. I, accordingly, desire that the following claims shall be accorded the broadest construction of which theirterms are susceptible in view of the limitations imposed by the prior art.

I claim as my invention:

1. A vacuum tight seal between an alloy comprising 28% to 34% nickel, 5% to 25% cobalt, less than 1% manganese-and the remainder iron, and a boro-silicate glass.

2. A vacuum tight seal between an alloy comprising 24% to 34% nickel, 5% to 25% cobalt, less than 1% manganese and the remainder iron, and a boro-silicate glass having an expansively of 3.0 to 6.5 (10 centimeters per centimeter per degree centigrade.

3. A vacinnn tight seal between an alloy comprising 24% to 34% nickel, 5% to 25% cobalt, less than 1% manganese and the remainder iron, and a glass having a composition of 73.8% $102 18. 820:; 52% PhD; 1.0% A1203; 0.5% AsaOa.

4. A vacuum tight seal between bore-silicate glass and an alloy having essentially iron, nickel and cobalt.

5. A vacuum tight seal between glass having an expansivity of 3.0 to 6.5 10-' centimeters per centimeter per degree centigrade and an alloy having essentially iron, nickel and cobalt.

6. A vacuum tight seal between a glass containing substantially 73.8% SiOz, 0.5% AS203; 52% PhD; 1.0% A1103; 18.7% B20: and an ironbase alloy containing substantially 29.8% nickel,

15.5% cobalt, 0.22% manganese and less than 0.1% carbon.

7. A vacuum tight seal between a boro-silicate glass andan alloy containing chiefly iron, nickel, cobalt, manganese and carbon'in such proportions that the present nickel contact plus 2.5 times thepercent manganese content plug 18 times the percent carbon content divided by the percent iron content is between 0.50 and 0.60.

81A vacuum tight seal between a conductor comprising an alloy containing substantially 24 to 34% nickel, 10 to 25% cobalt, less than 1% manganese and the remainder iron and a borosilicate glass containing 65 to 75% $102, less than 10% PhD, less than 6% A120: and 10 to 25% B203.

9. A vacuum tight seal between a conductor comprising an iron-base alloy containing substantially 29.8% nickel, 15.5% cobalt, 0.22% manganese less than 0.1% carbon and the remainder iron and a boro-silicate glass having an expansivity of 3.0 to 5.5 10- centimeters per centimeter per degree centigrade.

10. An electrical discharge device comprising at least two electrodes, insulation between said electrodes comprising glass having an expansivity of 3.0 to6.5 10 centimeters per centimeter per degree centigrade and an alloy having essentially iron, nickel and cobalt sealed vacuumtight through said glass.

at least two electrodes, insulation between said electrodes comprising bore-silicate glass and an alloy having essentially iron, nickel and cobalt sealed through said glass.

12. An electrical discharge device comprising at least two electrodes, insulation between said electrodes comprising bore-silicate glass and an alloy comprising 24 to 34% nickel, 5% to 25% cobalt, less than 1% manganese and the remainder iron, sealed vacuum-tight through said glass.

13. An electrical discharge device comprising a container having a wall portion comprising glass having an expansivity of 3.0 to 6.5 10- centimeters per centimeter per degree centigrade, and an alloy comprising 24 to 34% nickel, 5% to 25% cobalt, less than 1% manganese and theremainder iron, sealed vacuum'tight through said glass.

14. An electrical discharge device comprising a container having a wall portion comprising boro-silicate glass and an alloy comprising 24 to 34% nickel, 5% to 25% cobalt, less than 1% manganese and the remainder iron, sealed vac-' uum tight through said glass, said glass conv30 11. An electrical discharge device comprising i taining to S102, less than 10% PhD,

less than 6% A: and 10 to 25% B203.

HOWARD SCOTT. 

